With temperatures nudging 40 degrees in South Australia's south-east, a Mt Gambier vet says it's important for dairy farmers to keep their cows cool.

Andrew Hoare says cows pant to keep their temperature down in the same way that dogs do.

He says dairy cows will be seriously affected today because their body temperature is generally high.

"So their metabolic rate is high, so they produce a lot of heat within their body, on top of all the heat that is in the environment at that stage.

"So you can reduce some of the feeding to reduce some of the heat load, or provide a cool environment if you can - tree lines, under centre pivot irrigation, and changing the routine, changing when you milk them, so milking them later in the evening hopefully when it's cooler, and cooling the yards down and watering the yards down before you actually start milking."